Vacuum packing is a common method for storage, in which, a bag is evacuated to prevent decomposition or oxidation of the item therein by the ubiquitous bacteria in the air. Generally, when a user desires to vacuum pack food or the like using a vacuum bag, the food is put into a vacuum bag. Afterwards, air is drawn from the vacuum bag and an open end of the vacuum bag is sealed by a vacuum packing apparatus. However, some bags used in vacuum packaging are composed of two pieces of flat plastic films. The flat surfaces of the films are easy to be jointed together when the bag is evacuated, and thus makes air pockets be trapped in the bag, rendering the bag unsuitable for vacuum packaging of perishable items. In order to achieve a desirable vacuum, lots of efforts were made in the prior art.
One improved type of bags with embossments has been widely used in our daily life. A plurality of embossments each extends from the bottom to the open end of the bag is formed on the inner surface of the bag. When an item is vacuum packed, an air discharge path is defined by the embossments. However, when an item is put into the bag, an internal cavity may be formed between the bottom of the bag and the item. The air in the cavity will not be evacuated because the item obstructs the air discharge path. Thus a desirable vacuum cannot be obtained.
Another conventional type of vacuum bag is disclosed in Chinese patent publication No. 2736281, which has strip ridges (or grooves) on both plastic films thereof. The ridges (or the grooves) formed on the films are perpendicular with each other, and thus air flows along the channel defining by the ridges (or the grooves). However, forming the ridges (or the grooves) on both films makes the manufacturing process complex and costly.
Chinese Patent Publication No. 2312897 and U.S. Pat. No. RE 34929 disclose two conventional types of plastic bags for vacuum packing, which have ridges densely covered on one plastic film. When the bag is evacuated, air is extracted along the channels defined by two adjacent ridges. The channels are intercommunicated, so that there is no said internal cavity in the bag. However, in order to adapt for the use of sealer, the ridges formed on the bag are diagonal or curvilinear in the direction from the bottom to the open end of the bag, which results in that the air will not linearly extracted from the bag. So, it takes more time to evacuate the bag. Furthermore, the above described bags are of less strength, and they are easy to be destroyed when there is a breach on the film.
U.S. Pat. No. 6,991,109 titled “Vacuum Sealable Bag Apparatus and Method”, issued to Daniel P. Shannon on Jan. 31, 2006, also describes a storage bag with a venting strip formed therein to assist in evacuating the bag. The venting strip can be apertured and/or can have a textured or rough surface that creates channels between the inside surface of the storage bag and the venting strip, thereby allowing air to exit from the interior of the bag. However, the venting strip makes the manufacturing process complicated and is difficult to clean. Moreover, the strip may easily be cracked which makes the bag unsuitable for repeated use.